Radiation therapy is an accepted treatment for a wide variety of medical conditions. High intensity radiant energy sources in the visible band, such as lasers, are now being widely used for both internal and extracorporeal procedures. While the microwave band, between 300 MHz and 30 GHz affords the capability of penetrating deeper than visible light while interacting differently with body tissue it has heretofore been employed primarily only in a variety of dissimilar medical procedures.
Microwave energy exerts its effect on tissue through controlled regional heating (hyperthermia) of affected features through interaction between the wave energy and magnetically polarizable tissue matter. By using microwaves to establish a regional hyperthermia, it is possible to preferentially increase the temperature of diseased or unwanted histological features to levels which are pathologically effective. At the same time, a necessary objective is to maintain adjacent tissue at acceptable temperatures, i.e., below the temperature at which irreversible tissue destruction occurs. Such microwave induced hyperthermia is well known in the field of radiology where it is used in the treatment of individuals with cancerous tumors.
A number of specific methods for treating histological features by the application of microwave radiation are described in the medical literature. For example, a technique for treating brain tumors by microwave energy is disclosed in an article entitled “Resection of Meningiomas with Implantable Microwave Coagulation” in Bioelectromagnetics, 17 (1996), 85-88. In this technique, a hole is drilled into the skull and a catheter is invasively inserted into the hole to support a coaxial radiator or antenna. Microwave energy is then applied to the antenna to cause the brain tumor to be heated to the point where the center of the tumor shows coagulative necrosis, an effect which allows the meningioma to be removed with minimal blood loss. Another technique in which microwave energy is utilized to treat prostate conditions is disclosed by Hascoet et al. in U.S. Pat. No. 5,234,004. In this technique, a microwave antenna in a urethral probe connected to an external microwave generating device generates microwaves at a frequency and power effective to heat the tissues to a predetermined temperature for a period of time sufficient to induce localized necrosis. In a related technique disclosed by Langberg in U.S. Pat. No. 4,945,912, microwave energy is used to effect cardiac ablation as a means of treating ventricular tachycardia. Here, a radiofrequency heating applicator located at the distal end of a coaxial line catheter hyperthermically ablates the cardiac tissue responsible for ventricular tachycardia. As with the described methods of tumor treatment, this method of cardiac ablation operates by preferentially heating and destroying a specifically targeted area of tissue while leaving surrounding tissue intact.
While the general principle of propagating microwave energy into tissue for some therapeutic effect is thus known, such applications are usually based on omnidirectional broadcasting of energy with substantial power levels. The potential of microwave energy for use with subcutaneous venous conditions and skin disorders has not been addressed in similar detail, probably because of a number of conflicting requirements as to efficacy, safety, ease of administration and side effects.
As a significant number of individuals suffer from some type of subcutaneous but visible abnormality, therapeutic techniques which effectively address these conditions can be of great value. Such features which are potentially treatable by microwave energy include conditions such as excessive hair growth, telangiectasia (spider veins) and pigmented lesions such as cafe-au-lait spots and port wine stains (capillary hemangiomas). Of these conditions, excessive hair growth and spider veins are by far the most common, affecting a large percentage of the adult population.
Unwanted hair growth may be caused by a number of factors including a genetic predisposition in the individual, endrocrinologic diseases such as hypertrichosis and androgen-influenced hirsuitism as well as certain types of malignancies. Individuals suffering from facial hirsuitism can be burdened to an extent that interferes with both social and professional activities and causes a great amount of distress. Consequently, methods and devices for treating unwanted hair and other subcutaneous histological features in a manner that effects a permanent pathological change are very desirable.
Traditional treatments for excessive hair growth such as depilatory solutions, waxing and electrolysis suffer from a number of drawbacks. Depilatory solutions are impermanent, requiring repeated applications that may not be appropriate for sensitive skin. Although wax epilation is a generally safe technique, it too is impermanent and requires repetitive, often painful repeat treatments. In addition, wax epilation has been reported to result in severe folliculitis, followed by permanent keloid scars. While electrolysis satisfactorily removes hair from individuals with static hair growth, this method of targeting individual hairs is both painful and time consuming. In addition, proper electrolysis techniques are demanding, requiring both accurate needle insertion and appropriate intensities and duration. As with wax epilation, if electrolysis techniques are not performed properly, folliculitis and scarring may result.
Recently developed depilatory techniques, utilizing high intensity broad band lights, lasers or photochemical expedients, also suffer from a number of shortcomings. In most of these procedures, the skin is illuminated with light at sufficient intensity and duration to kill the follicles or the skin tissue feeding the hair. The impinging light targets the skin as well as the hair follicles, and can burn the skin, causing discomfort and the potential for scarring. Further, laser and other treatments are not necessarily permanent and may require repeated applications to effect a lasting depilation.
Like hair follicles, spider veins are subcutaneous features. They exist as small capillary flow paths, largely lateral to the skin surface, which have been somewhat engorged by excessive pressure, producing the characteristic venous patterns visible at the skin surface. Apart from the unsightly cosmetic aspect, telangiectasia can further have more serious medical implications. Therefore, methods and devices for treating spider veins and other subcutaneous histological features in a manner that effects a permanent pathological change to the appropriate tissues are highly desirable.
The classical treatment for spider veins is sclerotherapy, wherein an injection needle is used to infuse at least a part of the vessel with a sclerotic solution that causes blood coagulation, and blockage of the blood path. With time, the spider veins disappear as the blood flow finds other capillary paths. Since there can be a multitude of spider veins to be treated over a substantial area, this procedure is time-consuming, tedious, and often painful. It also is of uncertain effectiveness in any given application and requires a substantial delay before results can be observed.
Another procedure for the treatment of shallow visible veins, which is similar to techniques used in depilation, involves the application of intense light energy for a brief interval. This technique exposes the skin surface and underlying tissue to concentrated wave energy, heating the vein structure to a level at which thermocoagulation occurs. In particular, these energy levels are so high that they cause discomfort to some patients, and they can also be dangerous to those in the vicinity, unless special precautions are taken. In addition, some patients can be singed or burned, even though the exposure lasts only a fraction of a second.
Due to the serious problems that the subcutaneous abnormalities can create in individuals, there is a general need to be able to treat such features in a manner that effects beneficial pathological change without adverse side effects or discomfort. An optimal therapeutic technique should effect a permanent pathological change without requiring repeated applications to reach the desired effect. Moreover, these procedures should be noninvasive, should cover a substantial target area that is not limited to a single hair follicle or spider vein, and should make optimum use of the energy available. Finally, pathological changes should occur only in the targeted feature, and not in intervening or underlying layers.